Using pickaxes and backhoes to move large amounts of debris, rescue crews moved swiftly Tuesday to pull survivors from the rubble of a 6.1-magnitude earthquake in southwestern China that has already claimed more than 400 lives.

Groups of volunteers combed through debris with their bare hands in an area where more than 1,000 homes collapsed. One of those helpers was Jackson Zeng, who joined about two dozen classmates on a trip to Yunnan province's Ludian county, hit hard by the quake.

"I grew up around here and these are my people. I'm not sure what I can do, but I will help any way that I can," said Zeng, a third-year student at Kunming University of Science and Technology.

Now, residents have a new fear: at least one barrier lake, formed during post-quake landslides, is rising quickly and threatening to flood nearby homes. According to CCTV.com, the barrier lake formed between the towns of Ludian and Qiaojia when a landslide fell into the Niulan River.

Water and geography experts have been called to the scene of the rising water to analyze the situation, and in the meantime, residents downstream have been evacuated, CCTV.com also reported. The lake is some 330 feet wide and 1,600 feet long, and the water level has risen 130 feet so far and continues to rise, the report added.

Many hundreds of volunteers have converged on the nearby city of Zhaotong en route to the quake-hit areas – a typical phenomenon during disasters in China. Many came empty-handed, but some were formed into company-sponsored units complete with uniforms and their own relief aid to distribute.

The government also has sent thousands of tents, quilts, sleeping bags and cotton coats to the region, as well as folding beds, chairs and tables, and mobile toilets.

The quake struck an area of steep hills and narrow roads not suited to all the traffic of the massive relief effort, and heavy rain Tuesday added to the complications. Much of the damage was due to landslides.

Ambulances, bulldozers and trucks filled with water and noodles and the squads of volunteers clogged the main road heading to the hardest-hit town of Longtou, about 370 kilometers (230 miles) northeast of Kunming. Helicopters hoisted supplies to the most remote areas.

The Yunnan Civil Affairs Bureau said Tuesday that 410 people had been killed and 2,373 injured, with 12 people still missing about 48 hours after the quake. Rescuers pulled dozens of trapped people from the debris in the first couple of days.

A 5-year-old boy was dug from a collapsed home Monday, and on Tuesday, state media released a photo taken in a hospital of two pregnant women who comforted each other while trapped in the rubble before they, too, were rescued.

Many of the homes in Ludian, which has a population of about 429,000, were rudimentary mud-brick structures that collapsed easily in the quake.

Cai Jiangping, a 46-year-old corn farmer, pointed to where he and seven members of his extended family had lived on the other side of a river valley just south of Longtou.

"The house is a complete write-off. But we'll throw some plastic over it and then talk to the insurance company," he said.

Cai was sheltering with a group of friends, his motorcycle his only surviving possession.

Further from the worst-hit areas, landslides created barrier lakes where water levels were rising Tuesday to pose a new threat to about 800 residents and seven power stations downstream, where sudden flooding could prompt power outages, the official Xinhua News Agency reported.

The region is prone to earthquakes. In 1970, a magnitude-7.7 earthquake in Yunnan killed at least 15,000 people. In September 2012, a series of quakes killed 81 people.

In May 2008, a powerful quake in Sichuan province left nearly 90,000 people dead.